1. Field of the Invention
The invention relates generally to integrated circuits and more specifically relates to testing internal operational signals of an integrated circuit.
2. Discussion of Related Art
Electronic circuits perform a wide variety of designated functions for electronic systems. For example, integrated circuits may be used for data processing, data storage and retrieval, system analysis and control, and many other functions. Integrated circuits may be subject to programming, design, or operational errors, and internal operational signals are not exposed for acquisition by external devices during normal operation (i.e., they are internal to the circuit). It would be impractical or impossible to connect every internal operational signal to its own dedicated output pin of the circuit for monitoring purposes. As such, it is desirable not only to include logic in the circuit that performs the circuit's desired function, but also to include logic and components at the circuit for acquiring internal signals for debugging and testing purposes (e.g., for externally monitoring internal operational signals of the circuit). For example, the circuit may include a test signal routing hierarchy comprising test multiplexers (MUXs) having registers that can be programmed to select internal operational signals for routing through the test MUXs. The test MUXs provide the selected internal operational signals to test outputs (e.g., specialized General Purpose Input Output (GPIO) pins) for the circuit that are dedicated for debug purposes. Utilizing MUXs to output test signals that are normally internal to the circuit ensures that the cost and size of a circuit implementing testing logic is reduced, because MUXs allow a large number of internal signaling pathways to be condensed into a much smaller number of output signal paths. These test signal output paths may be monitored by a logic analyzer to acquire the selected internal operational signals.
Unfortunately, dedicated test signal output paths are expensive and occupy valuable space upon the die of an integrated circuit. Thus, circuit designers must constantly decide between building a circuit that is easier to debug, and building a circuit that is cheaper to manufacture. These conflicting goals cause continuing problems in the field of circuit design.
Thus it is an ongoing challenge to provide acquired internal operational signals in a manner that is effective yet at the same time reduces the expense of dedicated test signal output paths.